How NASA uses Revolution at Mission Control for Landsat 7 Satellite

In this case study, we look at how NASA uses Revolution to support the operation of their Landsat 7 satellite. We interview Ivar Tillotson, the Spacecraft Systems Engineer on the Landsat 7 flight operations team. Ivar is based at NASA's Goddard Space Flight Center, just outside Washington DC. The customer for this program is the United States Geological Survey.

The Landsat Satellite Program

The Landsat 7 Satellite is the latest in a series of spacecraft that have been collecting images from the Earth's surface for the past 35 years. It detects visible light and infrared and converts them into images. With a maximum resolution of 15 meters the images are suitable for many areas of research, including agriculture, geology, forestry, ocean reef conditions and Antarctic ice monitoring. The images are also used to assist with response to natural disasters such as fires, floods and earthquakes.

Landsat 7 images of southwestern Greece before (left, 7/18/07) and after (right, 9/4/07) this summer's severe fires.

Ivar explains how the long running nature of the program is of great benefit to researchers.

The Landsat family has used very similar instruments and flown in nearly identical orbits, allowing researchers an apple-to-apple analysis when comparing conditions over the past four decades. I guess 'consistency of product' is the best way to explain that.

The Revolutionary Swiss Army Knife

They use half a dozen Revolution built applications in support of Landsat 7 operations, most of which have multiple roles. As well as moving data around the center and processing it, each application has unique responsibilities. The most involved application is like a Swiss Army knife with a dozen software blades to do various Landsat 7 jobs . One of the most valuable modules in that application is the LoadChecker. Its vital that we check each command to ensure it will execute properly without harming any part of the spacecraft. Each day we load up 3000 to 4000 commands to the spacecraft. That's a lot of checking to do and it was always being done under a short deadline. LoadChecker peforms all the checks that used to be done, by three people for two hours each, in under five seconds.

Its vital that we check each command to ensure it will execute properly without harming any part of the spacecraft. LoadChecker peforms all the checks that used to be done, by three people for two hours each, in under five seconds.

Sleeping Easy at Night with Flight Automation

Revolution plays a huge role in our automation system. People used to have to be at work night and day to connect up to the tracking stations to watch the spacecraft data and notify the right people if something bad happens. Now there is no one working the night shift at Landsat 7.

The system is called Landsat On-Orbit Flight Automation, or LOOFA. LOOFA acts as an 'autopilot' to watch over the Landsat 7 at night when they'd rather be at home asleep. The Landsat 7 orbits the earth 15 or so times per day, with 10 to 12 of those orbits passing over one of the tracking stations. During these tracking passes we can observe how well the spacecraft is performing and send up commands to perform imaging and housekeeping activities. Passes last only about 10 to 12 minutes. Since the passes occur night and day, people used to have to be at work to connect up to the tracking stations to watch the spacecraft data and notify the right people if something bad happens. They wrote a system in Revolution to monitor these activities and tell people off-site if something wasn't right. The system sends out text messages specifying the problem immediately if one is found. That was the last piece of creating a viable automation system, and LOOFA became part of normal operations. Now there is no one working the night shift at Landsat 7.

Real Time Display and Processing

"We've built lots of Revolution applications that fill important needs" says Ivar. "One is a web application that lets us check on certain spacecraft activities while away from the office. Another is a real time display of where Landsat 7 is and which onboard commands it will execute next, along with other goodies like what time it will see the next tracking station and how close it is to running out of onboard commands. We started some of these applications as a pragmatic way to make some of our data more readable, then we started combining selected information from several files into one report. And then using the information to calculate new information snowballed like that. One of our Revolution applications has buttons for retrieving and processing the most current files from assorted directories on assorted computers, delivering the resulting files to different directories on different computer's transmitting some files out as email and printing others. The modules call each other to complete their own tasks. All the file manipulation is done to improve situational awareness by keeping the most current information together and easily accessible. And most of the actions happen automatically, based on timers or when products appear in a drop box."

Its not Rocket Science

We asked Ivar why NASA selected Revolution for this project. He explained how Revolution was particularly suited to doing the job. "Overall, the Revolution language is the key feature. Revolution is logical and intuitive, its easy to start small and build up features and capabilities and when things don't work right you are guided right to the problem. It's a high-level language with a low-level of frustration."

Overall, the Revolution language is the key feature. Its logical and intuitive, its easy to start small and build up…It's a high-level language with a low-level of frustration.

Overall, the Revolution language is the key feature. Revolution is logical and intuitive, its easy to start small and build up features and capabilities and when things don't work right you are guided right to the problem. It's a high-level language with a low-level of frustration.

Ivar went on to tell us how the needs of the space center change regularly and how Revolution helps them to keep up. "We have to deal with changes on the spacecraft, changes with our ground equipment, new priorities in image collection, almost every aspect of running the mission can change and we still have to fulfill our goal – keep generating quality images of the Earth. Whenever I need to add a new module I just open up Revolution and add a new button. There's a good chance I have an existing component that can be quickly adapted to fit the new role. For example I have a bunch of utilities that do all sorts of little esoteric jobs, for example extracting 32-bit chunks of data from 8-bit words, converting non-contiguous ranges and converting them using an outdated Air Force floating point method, deriving timestamps for each entry and…it goes on like that. Rapid development is the key, because if it takes longer to write and test the code than just to slog through the task by hand, is it worth writing the code?"

Revolution has a number of outstanding features too. There are so many ways you can optimize your code to get tasks done. The URL functions are so easy to use. I replaced something that used to take 50 steps to download data in an older language with a single line "put URL into URL ". When I first discovered this I practically did a dance through the office.

Of course there have been some frustrations along the way too. Ivar explained how there is no Daylight Saving time in the world of satellites. Shifting time for Daylight savings is irritating. Fortunately I was able to work around the issue with a little creativity.

 

Working at NASA

We asked Ivar what its like to work for NASA.

I've been working in spacecraft operations for the past 17 years, with 10 of them in Landsat 7. This is an evolving program, and I like that. The people I work with are very capable and we work together as an actual team and its hard to find a better situation than that. The operation and management of the Landsat satellites and image handling functions are under the purview of the U.S. Geological Survey. NASA built and launched the satellite in 1999 and in 2000 USGS assumed responsibility for its operation.

There is an amazing array of people using the Landsat data, because its available to everyone. Most scientific satellites produce data that is proprietary to a single researcher or group of researches and might be released to the public only after some period of time, if at all. Anyone can obtain Landsat images and use them without restriction.

An overlay of Capitan John Smith's map of the Chesapeake Bay on a Landsat 7 image of the Bay.

You can view some of the images produced by the Landsat here.

 

Landsat imagery courtesy of NASA Goddard Space Flight Center and U.S. Geological Survey